Brain function is based on the concurrent computation within and among nerve cells. At the level of the single nerve cell, information from thousands of synaptic inputs is received at dendritic spines, where it is processed by the dendrites' specific morphology and its distribution of voltage-gated ion channels. It is well established that the distributions of spines, dendrites and channels change with age -- both during normal aging and as a result of neurodegenerative diseases associated with aging such as Alzheimer's disease. For most neurons in the central nervous system, the details of how the dendrites transform information in normal and pathological states remain poorly understood. In large part this is because of the massively parallel nature of the connectivity between neurons -- it has not been possible to experimentally stimulate neuronal synapses in large numbers with well-defined spatial and temporal patterns that mimic the physiological input to the neuron. Here, we propose a new approach that will employ a novel imaging workstation allowing hundreds of individual synapses to be activated across the spatial extent of the dendrites by multi-site photolysis of caged neurotransmitter. This project will build on and make extensive use of our existing collaborative infrastructure that allows acquisition of the structure of a neuron in a brain slice, reconstruction of the neuron's morphology, construction of a compartmental model, and optical high-speed multi-site functional recording. We will use the morphological reconstruction to identify the exact sites for stimulation and recording. Computer simulations of the neuron will be used online to optimize experiments by identifying regions of the neuron meeting experiment-dependent specifications, and offline to aid in understanding the underlying ionic mechanisms of nonlinearities in the neuron's response to stimulation. - The goal of this project is to determine the input/output function of pyramidal neurons in the hippocampal area CA1. In order to accomplish this goal, the research objectives of this proposal are to: - Implement a workstation for concurrent optical multi-site stimulation and recording. - Refine structural imaging and morphological reconstruction to identify dendritic spines. - Improve neuronal simulations by iterative fitting of experimental data in small branches. Generate optimal multi-synapse activation patterns and investigate the neuron's activity generated by these patterns.